Recently, electronic watches have come into vogue incorporating calculator means having an electro-optical digitial display with the calculator constituted by integrated circuitry permitting the wrist watch to not only provide instantaneous time display but permit calculating operation. U.S. Pat. No. 3,803,834 teaches such combined wrist watch and wrist calculator.
The problem with such wrist watch calculators is not in the miniaturization of the components but in the manipulation of the calculator componentry by human hand. Technically and electronically, the watch and calculator industry has the ability to produce wrist watch calculator instruments as small as 1 square centimeter, essentially the volume of a single sugar cube. However, the display of the numbers requires a minimum of 2 square centimeters and, more importantly, the keyboard necessary to the hand operation of the calculator requires a minimum of 22 square centimeters for easy and comfortable operation. On the other hand, the size of the wrist watch or wrist calculator must be no larger than 3 centimeters in diameter and 7 square centimeters in terms of the face area of the watch or calculator face because a larger plate will not fit the normal person's wrist.
Therefore, in terms of U.S. Pat. No. 3,803,834 which mounts the keyboard to one face of the wrist watch or calculator case, the keys are of such a small size and the keyboard array is so reduced in size that it is almost impossible to operate the keys individually, and certainly such operation is neither easy or comfortable. Based on the limitations in watch case surface area of the face bearing the instrumentation and display, a minimum of 24 square centimeters is needed in terms of the display and keyboard requirements, but the surface of a conventional size watch or calculator case offers only 7 square centimeters, thus lacking 16 square centimeters or approximately 21/4 watch surfaces. In terms of the reference U.S. Pat. No. 3,803,834, a combined wrist watch and mini-calculator of that patent constitutes an essentially useless toy rather than a practical instrument.
It is therefore a principle object of this invention to provide a wrist calculator or combined wrist watch and wrist calculator in which the keyboard permits easy and comfortable operation as provided by an available surface area of the watch without compromising the surface area of the case required for display purposes.
It is a further object of this invention to provide an improved wrist calculator in which the wristband incorporates both the calculator keyboard and the batteries for powering the calculator componentry.
It is a further object of this invention to provide an improved wrist calculator in which the wristband may be separated to facilitate access to the keyboard defined by the wristband and to facilitate keyboard operation after removal of the wrist calculator from the wrist of the user.